Electric conductor with artificially increased self-inductance



July 23, 1929. u. MEYER 1,721,785

ELECTRIC CONDUCTOR WITH ARTIFICIALLY INCREASED SELF INDUCTANCE FiledNov. 17 1925 Petented July 23, 1929. l

PATENT OFFICE.

ULI'IIAS MEYER, F GOLOGNE-MULHEIM, GERMANY.

ELECTRIC CONDUCTOR WITH ARTIFIGIALLY INCREASED SELF-INDUCTANCE.

Application filed November 17, 1925, Serial No. 69,697, and in GermanyNovember 22, 1924.

It is well known that the prejudicial influence of the capacity can bedecreased by artificially increasing the self-inductance. Two differentmethods are in practice for this purpose. According to Pupin theincrease in the self-inductance is attained by the insertion of coilsinthe line and according to .Krarup a uniform increase in theself-inductance is attained by wrapping round the conductor a materialof high permeability.

Both methods have their drawbacks. In Pupins method the interrupteddistribution of the self-inductance leads vto undesirable consequenceswhile in Krarups method the 5 increase in the self-inductance ispossible only to a limited extent. Both methods have the drawback thatthe resistance is increased,

which increase is probably unavoidable.

There is a further method of increasing the self-inductance which may beconsidered to lie between the two methods above referred to. Accordingto this third method the self- 7 inductance is continuously distributedand can be increased to any desired value. If a 5 wire offerro-magneticmaterial a (see the drawing) is wrapped with a tape b serving as aconductor for the current a coil is obtained which has a very greatlength and a very small diameter and constitutes the line withartificially increased self-inductance. The

properties of such a line are very much dependent upon the angle ofinclination according to which the tape is wound helically around thecore. It is advisable to utilise the 5 space as'comnletelv as possiblebv wrapping the tape so that the windings shall lie verv close to oneanother. In this case the width of the tape determines the angle ofinclination of the helix. It is' immaterial forthe following dis ussionwhether the tape is or is the greater is the number of turns of thecoil;

accordingly the self-inductance per unit length of line rapidlyincreases when the angle of inclination decreases. However, there is atthe same time an increase in the resistance. The smaller the angle ofinclination, the longer becomes the path traversed by the current andthe smaller becomes the sectional area of the said path. According tothe present invention it is of utmost importance for the manufacture ofthe conductor to choose the correct angle of inclination, i. e. to makeit so that the gain obtained by increasing the self-inductance in anycase exceeds the loss caused by the increase in resistance.

Let a be the permeability of the ferro-magnetic material, 0' theconductivity of the outer covering, 9 the angle of inclination of thehelix, r, the radius of the ferro-magnetic material which corresponds tothe inner radius of the conducting covering, 7', the outer radius ofthis covering and a, and a, the angles of inclination for the radii r,and 1', and thus tgal 2'51'1 21"" For the resistance R and theself-inductance L we then get the following approximating formulae i sin(1 sin a, 092 sin (1 Sin a,

cos a L n 9,0! 10 H/Kn' As the main point is that the conductor shallhave an attenuation as low as possible, the angle of inclination must beso determined by taking into consideration the other constants of theconductor that the attenuation becomes a minimum. A certain clue maygenerally be obtained by proceeding as follows. If the formula validunder certain conditions for the attenuation constant is taken as abasis and the second term therein which increases with the root of theselflayers.

inductance is neglected, then the problem is simplified and only theposition of the minimum of 5% has to be determined. By using the lastformulae we find the condition for the angle of inclination to be tg aIf all the circumstances are taken into consideration we find that inorder to obtain the best form of conductor the angle of inclination hasto be between 30 and 70.

If the conducting tape has a great thickness, the current distributionwithin the tape is unfavourable, since the path of current is longer inthe outer layers and therefore the stream lines of the current threadsare compressed inwards. In order to avoid the increase in resistancewhich is thereby caused it is advisable in the case of thick conductors,to subdivide the tape and to arrange several layers which are connectedin parallel one above the other. However, this object is at tained onlyif the subdivision does in fact produce a more uniform currentdistribution. For this purpose it is necessary to adjust the angles ofinclination of the individual layers in such a manner that the currentdensity is as equal as possible in all layers. As shownby the formulaethis is very nearly attained if the angles of inclination and not thethickness of the tape are made nearly equal in all the The insulation ofthe individual layers from one another and similarly the insulation ofthe windings from one another need to be only very small, as thepotential difi'erence between adjacent points thereof is very small. a

The advantages of this kind of conductor viz. simple form of theferro-magnetic material, and consequently an easy subdivision thereof byusing bundles of thin wires, and easy thermic treatment-for improvingthe magnetic properties, can be fully attained only by using the correctangle of inclination according to the present invention.

In order to reduce also the hysteresis losses which become importanteven when the eddy-current losses are small, it is advisable to use amaterial in which the permeability depends upon the strength of thecurrent as little as possible, since according to a theory of Jordan thehysteresis losses areproportional to this increase in permeability withthe current.

A further improvement in this kind of conductors can be attained ifbesides the inner core an outer covering of ferro-magnetic material isemployed. By this means the self-inductance is further increased and inaddition thereto a good path is provided for the magnetic lines offorce, so that the efiect of the magnetic field outwardly is weakened.Preferably this outer covering is also subdivided into thin wires inorder to reduce the eddy current losses. If, as in the case of the core,these wires are laid parallel to the axis of the conductor they must besecured in position and this may be attained for instance, by windingthem helically around the conductor, the direction of the winding beingopposite to the direction of winding of the actual conductor.

The accompanying drawings illustrate two forms of construction accordingto the invention. In Figs. 1 and 2, a is the core of magnetic materialand b is the copper conductor in theform of a tape, which is woundaround the said core. In Fig. 2 a is an outer layer of magneticmaterial.

What I claim is v 1. A conducter wi'th artificially, increasedself-inductance comprising a core of ferromagnetic material and aflattened conductor intended to carry the current, which con ductor iswound helically around the said core with windings lying very close toone another and with an angle of inclination which is not less than 30and not greater than 70 for reducing to a minimum the attenuation of themain conductor with respect to the main frequency that comes intoquestion.

2. A conductor with artificially increased self-inductance comprising acore of ferromagnetic material and a flattened conductor intended tocarry the current which conductor is wound helically around the saidcore with windings lying very close to one another and with an angle ofinclination which is not less than 30 and not greater than 70 forreducing to a minimum the attenuation of the main conductor with respect to the main frequency that comes into question, and an outercovering of ferromagnetic material consisting of wires or tapes woundparallel to one another around the helically wound conductor.

In testimony whereof I have affixed my signature.

ULFILAS WYER.

